JPH1091250A - Device and method for adjusting temperature in low-temperature test chamber - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a double capillary entrance low-temperature chamber which is able to adjust temperature continuously from approximately 1.5K to approximately 400K. SOLUTION: A capillary 13 which is put at a distance from the test chamber 15, thermally insulated from a refrigerant, and heated controllably is arranged in a low-temperature reservoir 12. This capillary 13 has featured impedance to a flow of fluid. The entrance of a 2nd low-temperature and high-impedance capillary 72 is also in the low-temperature reservoir 12 and connected between the low-temperature reservoir 12 and test chamber 15. A combination of two entrance tubes which have different impedance from a control system having feedback of pressure and temperature enables the device to operate continuously and stably at temperatures within its operation range or shift over a predetermined temperature range.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

FIELD OF THE INVENTION The present invention relates generally to temperature regulation, and more particularly to regulating the temperature in a cryogenic test chamber to smoothly raise and lower the temperature of the test chamber throughout its operating range and to reduce any predetermined temperature. The invention also relates to an apparatus and a method for maintaining stable within its operating range for an infinite period of time.

[0002]

2. Discussion of the Prior Art The need to test various types of specimens for various properties has increased significantly in the last few years. Different methods have been devised to achieve such tests at cryogenic temperatures. Temperature regulation in low temperature test chambers requires a high balance between the supply and loss of thermal energy. Criteria for the efficiency of a particular control strategy are the width of the temperature range over which control can be maintained and the duration and stability achieved at temperatures within this range. In general, two different control modes of operation must be used to achieve accurate temperature regulation above or below the normal boiling point of the liquid cryogen medium used in the cryogen. This temperature is 4.2K in liquid helium ⁽⁴ the He) is a cryogen frequently used. However, temperature regulation near the normal boiling point is particularly difficult due to the large changes in the thermal properties (ie, specific heat) of the liquid itself that undergoes a liquid to gas transition in this temperature range. Temperature fluctuations that cause thermal instability are the most common problems encountered when attempting to control the temperature at the normal boiling point of a cryogenic liquid, generally when switching between low and high temperature control modes. .

[0003] In adjusting the temperature above the normal boiling point of the liquid coolant, heat is provided to the test chamber to effectively maintain and control the desired temperature. Because using a reservoir as a direct source and conditioning the test chamber at a higher temperature is quite uneconomical, the test chamber is typically thermally isolated from the environment at a lower temperature. Temperature regulation is then achieved by drawing a small portion of the liquid cryogen from the remainder of the cryocontainer, maintained under slight overpressure, through a passage such as a coupling tube into the test chamber. The pressure difference between the test chamber and the cryogen reservoir is
Entering the coupling tube, effectively providing the only injection mechanism for liquid cryogen through the test chamber required for temperature control. The fluid reaching the interior of the test chamber is then heated to the desired temperature, and steam flows through the test chamber to provide uniform temperature control. Although this control scheme is appropriate for high temperature regulation, its thermal response near the normal boiling point of the cryogenic fluid is somewhat due to the difficulty of passively controlling the evaporation flow rate due to overpressure present only in the cryogenic vessel. Not enough.

[0004] Temperatures below the standard boiling point of the liquid coolant are required
Continually draws heat from the test chamber
A second category of methods is used. With these methods,
Vapors where the temperature of the test chamber is above the liquid phase cryogen
Reduced by applying a vacuum to the
Lower its boiling point temperature. liquid^FourHe is used as a low temperature medium
In practical applications, the temperature should be lower than its surroundings.
The test chamber reached is thermally separated from the main bath in the cryocontainer.
Separated. This is above the liquid helium bath in the cryocontainer
Simply pumping steam is very expensive
It is. Because about 40% of the liquid is from 4.2K
1.5K to a large change in specific heat over this temperature range
In order for this to cool, it must be evaporated
This is because Therefore, most of the liquid helium is
At the normal boiling point of the main bath
Pumping only a small amount of helium into the test chamber
Better efficiency is achieved by the use of a wire. Tess
Liquid accumulated in the chamber ^FourHe is next
To a suitable pressure so that the system boils at the desired control temperature.
Will be issued. However, in most practical applications
Is a test available for accumulating cryogen in liquid form
Limited chamber volume (typically 10-10
20 cubic centimeters), liquid^FourFrom the standard boiling point of He
The lower temperature is only for a limited time, if the lowest temperature is 4
It can only be adjusted from 0 to 50 minutes. Test cha
When the liquid cryogen collected in the chamber boils and evaporates,
The system draws more liquid cryogen into the test chamber
The filling process must be restarted to take advantage
Thus, the effective temperature control is interrupted. Enough liquid
Only desired if cryogen is recollected in test chamber
The temperature can be reached again and adjusted. Proper shortage
Select pressure (underpressure) and maintain that pressure
Drain the test chamber when the liquid boils
Continue to let the desired temperature drop to about 1.5K
Can be achieved. The prior art of such low-temperature test equipment
An example of the device is shown in U.S. Pat. No. 4,848,093.
You.

This patent reduces the temperature of the test chamber in the cryocontainer by about one unit by a controllable heated capillary spaced from the test chamber but still located in the cryogen in the cryocontainer. .5K to about 30
A device for adjusting the temperature to between 0K is disclosed. The capillary regulates the flow of fluid from the cryocontainer to the test chamber so that the desired temperature is achieved in the test chamber. In the high temperature mode of operation, the heated capillary supplies a cryogenic fluid in the form of a gas, preventing any fluid in the liquid phase from entering the test chamber. In the low temperature mode below 4.2K, the capillary is heated to an extent that allows very little gas flow to the test chamber after the test chamber is filled with liquid cryogen.

[0006] This prior art device is shown here in FIG. 1, wherein the temperature regulating device comprises a reservoir 1 of liquid phase fluid.
Cryogenic vessel 11 adapted to contain cryogenic 2 at low temperature, a capillary 13 disposed in the cryogenic vessel, and a capillary heater means 14
A test chamber 15 within the cryocontainer but spaced from the capillary; a coupling tube 16; and a coil 17 defining a fluid flow path between the capillary and the test chamber.
And a coil 21, a test chamber heater 22, and a discharge means 38, which typically includes a variable flow through flow valve, a suitable pressure sensor, and a pump regulated by a readout device. The test chamber is partially evacuated to draw fluid from the cryocontainer into the test chamber via capillaries, coupling tubes and coils. Appropriate microprocessor controls are used to correlate heater and vacuum pump operation to temperature readings.

[0007] The device of this prior art patent regulates the temperature of the test chamber by maintaining the fluid therein at a desired temperature. In the high temperature mode, the capillary heater warms the capillary enough to bring any liquid flowing into it to the boil, causing the phase of the fluid to separate from the liquid phase as the fluid is drawn into the test chamber through the capillary. Change to gas phase. The test chamber heater warms any gas in the test chamber to the desired temperature, and then the gas moves upward to provide uniform temperature control along or throughout the test chamber.

In the intermediate temperature mode (about 4.2K), the fluid remains in the liquid phase without experiencing any net change in temperature as it is drawn into the test chamber via the capillary. The fluid is therefore maintained at a low temperature in the test chamber.

In the low temperature mode, as drawn from the capillary into the test chamber, the fluid remains in the liquid phase until a reservoir of liquid has accumulated at the desired level in the test chamber. The capillary heater then rapidly warms the capillary sufficient to effectively create bubbles or vapor locks, thereby substantially preventing fluid flow through the capillary. There, the evacuation means reduces the pressure in the test chamber enough to reduce the boiling temperature of the liquid therein to the desired temperature, and continues to exhaust the gas that forms when the liquid is boiling, thereby At a desired temperature of less than 4.2K.

The temperature of the test chamber is set to room temperature (about 300
The time required to lower with this prior art device from K) to a low temperature of about 1.5K would be about 30 minutes under normal circumstances. This low temperature can then be maintained for only about 30 to about 60 minutes, after which recharging and recirculation is required according to the teachings of the prior art.

Although this device worked well for many purposes, it was not possible to maintain the low temperature at a controlled level of less than 4.2K for long periods of time, for example, hours or indefinitely. Some tests cannot be completed in the 30 to 60 minutes provided by such prior art devices before recirculation is required. Of course, loss of temperature stability can adversely affect the specimen itself, resulting in inaccurate test data.

The first step that has been proposed to extend the temperature range of the cryostat is regulated by a thermally isolated small capillary inlet with adequate flow impedance and a mechanical valve in the cryocontainer. By providing a combination with a second inlet to the test chamber reservoir at the inlet of the temperature controlled test chamber. Thus, a small capillary is used to provide continuous filling of the reservoir below 4.2K when the valve is closed, and a second capillary is used to provide rapid cooling when the valve is open. It is possible to obtain a large flow through the inlet. Unfortunately, the difficulty of making a reliable cryogenic valve limits the commercial viability of this approach. An alternative that has been used is to remotely place a mechanical valve outside the cryocontainer. This configuration requires an inlet that is repositioned outside the cryocontainer via a mechanical valve.

[0013] Although this device is to be achieved in principle the temperature range of about 400K to about 1.5K (if liquid ⁴ He is used), temperature control in the vicinity of 4.2K is somewhat unsatisfactory. The long inlet utilized in this configuration results in a long waiting time to maintain and regulate the temperature. This might not make serious problems at temperatures above or below the boiling point of ⁴ the He, requires temperatures mode rapid thermal change is rapid control of properties of the liquid 4.
Significant instability occurs around 2K.

The purpose of testing specimens at low temperatures or at temperatures that must be maintained at some level between about 1.5K and about 400K is many and extensive. Some may include life testing. It would be achieved if observations could be made over a period of days or weeks. A detailed sweep of the magnetic or physical properties of a new or unknown test specimen may require a temperature sweep between 15K and 400K or within a subsegment that includes the temperature range. It is important that the temperature be controlled smoothly as it varies over the operating range, as signs of important intrinsic physical properties of the test specimen material can occur suddenly or discontinuously at some temperatures. In addition, careful testing, even at the lowest temperatures achieved by the device, may require long measurement times. For this reason, the temperature is continuous,
That is, it is important that it can be maintained indefinitely. Any known integrated prior art device smoothly circulates back and forth between all of these objectives, ie, between about 1.5K to about 400K, and selectively and indefinitely maintains any temperature within that range. Inability to achieve ability.

[0015]

SUMMARY OF THE INVENTION It is a primary object of the present invention to provide a low temperature test apparatus that allows for smooth and continuous circulation of test chamber temperatures from a minimum of about 1.5K to a maximum of about 400K, and in the same apparatus, The ability to quickly achieve either high or low temperatures and to stably maintain such temperatures for an infinite period of time.

[0016] This device is a cryogenic fluid.
) Includes a thermally isolated variable temperature impedance capillary that preconditions the cryogenic fluid before flowing into the isolated test chamber. The second, more capillary high impedance, gives the major source of cryogenic fluid in the liquid phase in the test chamber, such as is required for continuous operation at low temperatures (less than ⁴ 4.2K in the He). The novel combination of the present invention produces and continuously maintains a temperature in the test chamber ranging from about 1.5K to about 400K,
To the ability to circulate smoothly over the entire range of to 400K.

The apparatus of the present invention utilizes the basic structure and operation of the aforementioned low temperature test apparatus of US Pat. No. 4,848,093, with significant differences. In addition to the first temperature-controlled capillary, which feeds the other tubing through the cryogen reservoir as it enters the test chamber, a second capillary is connected from the cryogen reservoir to the test chamber via the protective filter only. Connect directly. Substantially all of the length of this second capillary is thermally and physically separated from the cryogen in the cryogen vessel. A second cryogenic fluid input and appropriate enhanced control allow any desired temperature within the full range of 1.5K to 400K to be achieved in the test chamber and maintained indefinitely. The second cryogenic fluid input or impedance is maintained separately from and separate from the cryogenic fluid bath in the cryogen vessel except for its input end. It has an impedance to the flow of cryogenic fluid that is much higher than the impedance of the first capillary. Due to the relative impedance of the two fluid flow means providing the supply from the cryocontainer to the test chamber, the present invention allows any temperature to be stably maintained within its test range, from the lower end of the range. Facilitates smooth circulation of test chamber temperature to the top.

Controlled by a suitable microprocessor controller, the combined method of operation of the two fluid flow impedance means allows for the full range of test temperatures to be achieved. At temperatures above about 4.2K, the test chamber experiences a relatively small underpressure and the first capillary is heated sufficiently that all of the cryogen flowing through the capillary to the test chamber is in gaseous form. Is done. Thus, the test chamber heater can raise the temperature of the gas in the test chamber to a desired level and maintain that temperature. Due to the relatively high impedance of the second capillary relative to the impedance of the first capillary, it is drawn into the test chamber via the second capillary in the high temperature mode;
The cryogenic fluid in liquid form is very low. If low temperature operation (between 1.5K and 4.2K) is desired,
A fairly high level of underpressure is maintained in the test chamber, while the first capillary is heated to an even higher level, creating bubbles therein, except for a very small amount of gas from the first capillary to the test chamber. Prevent inflow. The cryogenic fluid in liquid form is continuously and directly drawn into the test chamber via the second capillary and reaches the test chamber at a temperature lower than 4.2K by adjusting the level of vacuum. For this reason, about 1.5
The desired temperature can be achieved in a relatively short time upon cooling from a high temperature at a level between K and about 4.2K, so that the temperature can be maintained indefinitely.

For a cycle between two temperature points within the operating range of the device, the range is from about 1.5K to about 400K,
The microprocessor controller operates in rapid feedback fashion with the temperature sensor, heater element and vacuum pump to provide a smooth transition over the desired temperature range within the test chamber.

[0020]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The objects, advantages and features of the present invention will be more readily understood from the following detailed description when read in conjunction with the accompanying drawings.

The present invention provides an apparatus and method for continuously adjusting the temperature of a test chamber in a cryocontainer at a level between about 1.5K and about 400K with a dual capillary inlet configuration. This is achieved by using a constant flow of coolant medium to the test chamber in the gas or liquid phase and maintaining the medium at the desired temperature. A method for temperature regulation in a test chamber according to the present invention actively controls the supply of liquid coolant by partially evacuating the interior of the test chamber to approximately 1 psi above atmospheric pressure, or absolutely. At 16 psi on the scale, a normal steady state pressure difference from the rest of the cryocontainer is created. When combined with a new integrated dual inlet device, this technology results in a rapid thermal response of the system, facilitating temperature control and stability near the normal boiling point of the liquid coolant, high temperature control mode and low temperature control Eliminates fluctuations and temperature hysteresis normally encountered when switching between modes.

The apparatus of the present invention is disclosed in Japanese Patent No. 4,848,09.
No. 3 operates using the basic system and teachings, but maintains low temperature operation indefinitely, transitions smoothly and continuously over any temperature range within its operating temperature capability, Have significant improvements and modifications that allow other temperatures to be maintained in a stable manner at or above the normal boiling point of. One important advantage of the present invention is that it does not operate on a batch-by-batch basis, possibly requiring refilling or recirculation. Batch-based operation of some prior art devices causes the internal temperature of the specimen to change randomly within the test chamber during the recirculation process. The present invention not only allows more efficient operation because there is no interruption in recirculation, but also makes the measurements and readings much more accurate because the specimen being tested remains at the test temperature during the test. Thus, the test procedure does not affect the specimen as much as the previous known low-temperature test equipment and avoids spurious test data, while allowing a wide range of operating modes from a low temperature of about 1.5K to a high temperature of about 400K and its operation Allows smooth circulation over any part of the range.

The temperature versus time plots of FIGS. 4-6 illustrate the limitations of the prior art and how the present invention is superior. FIG. 4 shows how the temperature of the test chamber is non-linear as it drops from 10K to about 3K in a typical prior art device. There is a relatively rapid drop from steady state 10K to about 4.2K and the temperature is 4.2K.
Recovery or bounce 86 occurs when passing through. Next, there is a long intermediate state 85 in which the liquid cryogen fills the test chamber, and then the temperature may drop below 4.2K.
A slight rise 87 occurs when the flow of the cryogen through the variable impedance is interrupted, followed by a steady drop to 3K as shown here. Of course, the length of time that the sub-boiling point can be maintained is limited.

FIG. 5 shows the recovery of the test chamber from a temperature below 4.2K to a temperature above 4.2K. 4.2 temperature
Note the non-linearity and multiple bounces 91 when it is not possible to move smoothly through K to higher values. About 10
3. The temperature of K is shown at 92, which is shown at 93.
Non-linearly reduced to temperatures above 2K.

A plot of the temperature drop from 10K to about 2K, and vice versa, as is possible with the present invention, is shown in FIG. Note that there is linearity in all transitions, even when the temperature passes 4.2K from either direction. Downtime 95 at 2K or other levels below 4.2K can be indefinitely long. A length of about two minutes is shown here for illustrative purposes only. The purpose of FIG. 6 is therefore to show the linear temperature transition capability of the present invention. The rate of transition over the indicated temperature segment is approximately 1
K / min.

The prior art of FIG. 1 (from US Pat. No. 4,848,093) will now be described in more detail. The cryogenic vessel 11 contains a cryogenic fluid 12 having an upper surface 23 therein. The container 11 includes an airtight cover 24 having an opening through which the cryostat 25 extends. The controllably heated (variable impedance) capillary 13 and its heating element 14 are contained within a separate impedance capsule 26. The entire capsule and the fluid flow means 16, 17 and 21 projecting from the capillary 13 are maintained inside the vessel 11 below the surface 23 of the cryogenic fluid 12. The reason that the inlet to the coupling tube 16 via the capillary 13 is separated from the cryogenic fluid is to prevent unnecessary heating of the fluid bath as the capillary is heated for operational purposes.

The capsule 26 is preferably formed from a tubular body 27 closed at the top end by a cap 31 and at the bottom end by an annular cap 32.
Inner tube 33 extends through cap 32 and is closed at end 34 adjacent and spaced from cap 31 of tube 27. The inner tube 33 has a bottom opening 35 through which the coupling tube 16 extends. To separate, the annular portion of tube 27 is evacuated by evacuation tube 36, the end of which is closed during the manufacturing process. The heater 14 is typically a capillary 1
3 including a resistive wire wound around
Rapidly heats very small capillaries when applied by 7. Wire 41 connected to the capillary represents a temperature sensor connected to the control means as described below.

The cryostat 25 includes an outer container or shell 42 closed at the bottom by a cover plate 43 and having an annular seal 44 at the top.
4 fastens the cryostat to the cover 24, through which other elements of the cryostat pass in a sealed manner. Fluid conduits 16 and 17 have bottom cover 43
Extending through a suitably sealed opening therein. Shell 4
Within the 2 is a test chamber 45, which is connected to the fluid conduit means from the capillary 13 by the end 46 of the coil 21 extending through an opening in the cover 47 of the test chamber 45. In the test chamber 45,
There is a sample tube 51 whose bottom is sealed by a plug 52. Extending below the plug 52 in the test chamber 15 is a heating element 22 to which power is applied via a wire 53. A temperature sensor 54 connected to control means via a wire 55 is attached to the plug 52. Reference numeral 56 designates a sample to be tested by the apparatus of the present invention, the sample typically being suspended from the top 61 by a cable 62.

The sample tube or test vessel 51 is evacuated via an outlet 63 by a suitable vacuum pump (not shown). A thermally conductive inert gas is then introduced into the sample tube 51 and the sample tube 5 is contacted with the specimen 56 and the cryogenic fluid in the test chamber 15.
1 to provide thermal contact with the wall. Is thermally conductive,
A typically used substance that maintains the gas phase at low temperatures is helium. Here, typically cold fluid used is helium ⁽⁴ He). The temperatures discussed here relate to helium as a cryogenic fluid. However, other cryogenic fluids may be used and their characteristic temperature, specifically their boiling temperature, will be adjusted accordingly. The cryostat test chamber, separated from the cryogenic fluid reservoir by a shell 42 vented to a background pressure of less than 1 millitorr, is preferably filled with any suitable separation material, such as aluminized mylar.

The capillary 13 in the impedance chamber 26
Effectively includes the impedance aspect of the flow of the cryogenic fluid from the reservoir 12 to the test chamber 15. The inner diameter of the capillary 13 is about 0.1 mm and has a length of about 10 mm or less. The coupling tube 16 extending from the capillary 13 is about 0.6
mm inside diameter. The diameter of the inner tube 35 is typically about 1.4 mm and has a length of about 100 mm. While these dimensions have been found to give satisfactory results, it is clear that other dimensions may be used and that these are for illustration only. Of course, capillary 1
3 must be dimensioned to match the intended proportion of the mass flow of fluid into the test chamber in order to provide cooling for the specific purpose of the device of the invention. For the specific dimensions given, (about 1 mm
Pump vigorously (above Hg) and capillary heater 14
Alternatively, when no heat is provided by the heater element 22, a fluid mass flow of about 1 cubic centimeter per minute of liquid helium can be achieved.

The capillary heater element 14 is preferably
It is made from a material such as phosphor bronze resistance wire having a diameter of about 0.08 mm. Temperature sensor 41 may be made of a superconducting niobium-titanium alloy or the like (as described in more detail below). The outer tube 27 of the impedance chamber may be formed from any suitable material, such as brass, stainless steel, and the like. Inner tube 33 and coupling tube 16 are preferably made of a material with low thermal conductivity, such as stainless steel or cupronickel (CuNi). The coupling tube 16 may be formed into a first coil 17 remote from the impedance chamber 26 but still within the cryogen reservoir 12. This provides cooling of the fluid flowing therethrough from the capillary to the test chamber by thermal contact with the cryogenic fluid. The coupling tube also optionally includes a second coil 21 in a separate container 42. This helps to achieve thermal separation between the test chamber 15 and the cryogenic fluid 12.

As an example of the effectiveness of the capillary heater 14, the application of about 0.1 watts of power to the heater coil raises the temperature of the capillary 13 to about 300K in a matter of seconds. Lesser amounts of power may be applied to achieve lower levels of heat as required for operation of the device as described in more detail below.

In operation, for explanation purposes 4.2.
At a test chamber temperature above K, the boiling point of the cryogenic fluid, sufficient heat is applied to the capillary 13 to boil the liquid flowing therethrough. Test chamber 1 from reservoir 12
Note that the fluid flow to 5 depends on the level of vacuum or underpressure achieved by vacuum pump 38. Also note that this type of device typically maintains an overpressure on the cryogen level 23 of about 1 psi above normal pressure. This is pump 3
A very small amount of vacuum provided by 8 is combined with an overpressure above the cryogenic fluid 12 to allow the test tube 1 to flow from the reservoir via the capillary and conduit 16.
5 means to cause a fluid flow. The level of vacuum provided by pump 38 is a critical aspect of the present invention, as will become apparent. If a relatively small amount of heat is applied to the capillary 13, the cryogen flows through the tube only via the coupling tube 16 and the coils 17 and 21 into the test chamber 15 in gas phase. Although the temperature in the heated capillary is above 4.2K, when gas passes through the tube 16 and the coil 17 in the fluid reservoir 12,
5 is cooled so that the gas entering it is approximately 4.2K.
At this point, the heating element 22 can raise the temperature of the gas in the test chamber to any desired level, 400K, which is above room temperature.

As described in US Pat. No. 4,848,093, if it is desired to perform the test at about 4.2K, a cryogenic fluid in liquid form is passed through the capillary 13 and coupling tube 16 to the test chamber. Almost 4 to 15
As at 2K, neither heating element 14 or 22 is activated, and a very low level of vacuum is provided to pump 38. In theory, this is as long as desired.
2K can provide a continuous test temperature. In practice, it is very difficult to maintain a cryogenic fluid at the boiling point without significant temperature discontinuities arising from the transition between the liquid and gaseous states. The present invention provides a means for controlling the test chamber temperature to a desired level without discontinuities.

Finally, the temperature in the test chamber is set to 4.2
If it is desired to achieve below K, cryogenic fluid in the form of a liquid will pass through the capillary 13 and the coupling tube 16 to the test chamber 15 where the amount of the liquid will increase in the test chamber. If the amount of cryogenic liquid is stored in this test chamber in the desired amount, relatively high heat will be applied through the heating element 14, thus creating a restrictive bubble effect or vapor lock and the flow of liquid The liquid in the capillary 13 immediately boils in such a way that is completely isolated from the test chamber. There is a small residual flow of gaseous cryogen through the capillary, which is negligible compared to the amount of fluid passed in liquid form,
That is a reduction of 0 times. The pressure in test chamber 15 is reduced as needed to reduce the boiling point of the liquid therein to the desired temperature, as low as 1.5K. Mechanical pump 3
With a relatively large pump (such as a diffusion pump) instead of 8, the boiling point can be reduced to values as low as 1.3 K, but this is impractical for most purposes. In low temperature operation, testing can continue at a temperature below the atmospheric boiling point of the cryogen (4.2 K), as long as the cryogen in liquid form is in the test chamber. Liquid cryogenic fluid is applied to the test chamber 15
If discharged within, the test must be interrupted,
The described test procedure is recirculated.

Referring now to FIG. 2, the double capillary inlet configuration of the present invention will be described in detail. In addition to the appropriate additional control functions described with respect to FIG. 3, the structural differences relate to the second capillary inlet shown in the lower right part of FIG. The structure previously described with respect to FIG. 1 is all incorporated into the device of FIG. 2, and thus this structure is not further described except for its improved structure and its functional aspects relating to operation.

The dual capillary configuration of FIG. 2 allows a constant supply of cryogenic fluid to enter the test chamber in a gas or liquid phase such that it is appropriate for operation at a particular temperature. The desired temperature can be achieved quickly and accurately and maintained accurately. The steady state situation is that an overpressure of about 1 psi above reservoir surface 23 is a normal condition. This lower level of underpressure in test chamber 15 does not substantially affect the normal boiling point of the cryogenic fluid. Appropriate adjustments are made to the level of vacuum provided by pump 38 and heating elements 14 and 22 to provide the full range of functional operation of the apparatus of the present invention of FIG. 2 as previously described. Pump 38 includes a valve that is adjusted to change the applied level of vacuum rather than changing the speed or other operating characteristics of the pump itself. Pump 38 includes an integrated valve arrangement.

The upper or inlet end 71 of the second thermally isolated capillary flow impedance tube 72 connects into the test chamber 15. Insignificant portion of lower end of impedance tube 72 and inlet filter 7
Only three are immersed in the cold reservoir 12. The filter is preferably made of sintered copper felt, e.g.
Particle collection size. This filter provides impedance inlets due to frozen air or hydrogen or other particulate matter that can impede fluid flow within tube 72 if tube 72 is opened directly to fluid reservoir 12, ie, possible clogging of capillary 72. It only has a mechanical function to prevent Tube 72 may be 101 mm or more in length from filter 73 to the entrance of test chamber 15. The diameter of this second impedance capillary conduit is the same as that of the capillary 13, ie about 0.1 m
m. However, this is the
By inserting a wire 74 having an outer diameter of 0.075 mm inside the portion of mm or more, a considerably high flow impedance is formed. This is much less than 0.1 mm of the capillary 13, with a cross section of only about 0.0
Leave a 25 mm path. The size of the cold capillary inlet 72 is
4. Provide sufficient cooling to balance the thermal load entering the test chamber, provided by the capillary 13 even at high temperatures for test temperatures of less than 4.2 K and even when essentially blocked. Must be chosen to bring. If the impedance is too high, there is insufficient cooling and no liquid accumulates in the reservoir of the test chamber. If the impedance is too low, more liquid than necessary flows into the test chamber, thereby preventing the desired low temperature from being reached.

In operation, 4.2K as described above.
At higher temperatures, the underpressure in the test chamber 15 provided by the pump 38 is at a relatively low level, and the gaseous cryogen flows into the capillary 13 and the coupling tube 16.
To be easily drawn into the test chamber via the Because the impedance of the capillary 72 is high and only liquid cryogen in the liquid phase passes through this high impedance inlet, the liquid cryogen substantially reduces the test chamber 15 when the device of the present invention is operating at higher temperatures.
Do not enter. For low temperature operation below 4.2K, the capillary 13
Is almost completely shut off by the relatively high temperature applied to it (approximately 300K), which results in vapor lock due to the rapid and complete boiling of the cryogenic fluid in contact with it. To operate at low temperatures, it is necessary to apply a relatively high level of vacuum of 1 mmHg or more or 0.01 psi absolute. Due to the relatively high impedance of the capillary 72, the maximum liquid helium flow for this example is about 400 cc / min. As long as a high level of vacuum is maintained, the liquid cryogenic fluid flows through the high impedance capillary 72, and temperatures as low as 1.5K can be achieved in the test chamber 15 and maintained indefinitely. At such a high level of vacuum, the low temperature in tube 72 is less than 4.2K. Since the cryogen in tube 72 is not exposed to the reservoir, the cooled liquid is 4.2K.
Not risen.

If it is desired to maintain the temperature of the test chamber at about the critical point of 4.2K, the level of vacuum maintained by pump 38 is slightly less than the 1 psi pressure maintained at the standard pressure in the reservoir. Only. For the purpose of maintaining the temperature at about 4.2K, about 73
A vacuum level of 6 mmHg or 14.23 psi is applied. This allows the liquid cryogen to be drawn through the high impedance tube 72 without causing a substantial drop in the boiling point of the liquid so that 4.2K continuous operation can be maintained. This is a variable impedance capillary 13
Are all maintained in shutdown mode for temperatures below 4.2K. As mentioned above, even in the shut-off mode, there is a slight leak of gaseous cryogen through the capillary 13 and therefore the coupling tube 16 and the capillary 13
There is a percentage of liquid helium loss that is determined by the heat leaking into the test chamber through. The cold high impedance inlet 72 counteracts the predominant heat load in the test chamber by continuously drawing cold liquid helium from the cold reservoir 12. Liquid from the reservoir 12 at a pressure differential of about 1 psi is isentically spread via the impedance 72, thereby reaching the test chamber at a temperature below 4.2K of the reservoir. The heat transferred from the main reservoir 12 via the liquid in this column and the heat from the device (warmer at the top outside the cold bath) balances the cooling power of the available cooling system from the potential heat of evaporation. Note that the cold reservoir in the test chamber 15 continues to fill under these conditions until

The structure described above with respect to FIG. 2 allows continuous operation of the cryogenic test chamber of the present invention at a desired temperature in the range of about 1.5K to about 400K without significant temperature changes for an infinite period of time. To Further, the test chamber may be cycled in a temperature range within the full range of 1.5K to 400K. That is, if it is desired to perform a magnetic measurement test on the sample, for example, by smoothly varying the temperature between 3K and 50K, the apparatus can do so.

The control arrangement of FIG. 3, together with the structure of FIG. 2, enables the achievement of tests not previously available with the low-temperature test arrangements known in the prior art. Controller 75 of FIG. 3 is preferably a multi-channel, microprocessor-based programmable measurement and control unit (commonly referred to as an R / G bridge). In general, the controller 75 can accurately measure and control temperature using different types of temperature sensors over a wide dynamic range. As an example and a preferred embodiment, the controller 75 includes two independent proportional-integral deviations (P.I.
D. ) Incorporates two 15 watt power control channels that are externally regulated by a software controller. A full computer type system 76 coupled to a controller 75 via a suitable interface 77 (such as a GPIB interface) is typically used, I. D. Operating the temperature control software based on the user interface to provide the user with an interface to achieve the desired purpose of the embodiment of FIG. The presence of the host computer 76 in the control system of FIG. I. D. Easy storage and manipulation of time constants, gains and other process variables is provided. The two control channels of 15 watts in the controller 75 use the feedback information gathered by the thermometer 54 to accomplish the commands received from the user via the link 77 to regulate the heater 22, pump 38 and valves. . Extensive firmware resident in the memory (ROM) 81 in the controller 75 is linked by a control software resident in the computer 76 to a link 77
A simple but powerful set of enforcement commands passed through is used to configure complex control systems. Thermometer 54
The calibration file (temperature reading corresponding to the thermometer resistance value) is I.
D. The transition from resistance to temperature is accomplished in the controller 81 prior to the effective temperature control achieved by the software resident based on This design significantly enhances the overall control response of the system,
The control P. I. D. Is not affected by nonlinearities in the resistance normally associated with the temperature response of the thermometer 54. As a practical matter, the ability of the linear input provided by the controller 75 to the temperature feedback reading via the link 77 results in a tighter control loop adjustment by the control software resident in the computer 76. As described below, this configuration can be
The embodiment of FIG. 2 provides a smooth transition of the control temperature within any sub-segment of the temperature range of the device.

In accordance with the present invention, without the need for intermediate conditions frequently required by prior art systems to collect liquid in a test chamber, the control system includes:
It provides a smooth transition across 4.2K and the ability to maintain temperatures above 4.2K, 4.2K or below indefinitely. As noted above, the intermediate state was required in the prior art to achieve lower temperatures and maintain stability, generally below 4.2K. As a practical matter, the intermediate state 85 typically lasts for perhaps a few minutes (10-20 minutes), as shown by the plot of temperature versus cooling time in FIG. Probably done to start. The low temperature mode includes conditions where reduced cryogen gas flow within the test chamber 15 is achieved with the establishment of a high vacuum level. At the end of the intermediate state, the control system will apply the appropriate vacuum level to achieve the desired target temperature as read by thermometer 54. However, due to the long time required to achieve the required settings of hardware and software appropriate for the low temperature mode, temperature fluctuations 91 (FIG. 5) causing thermal instability cause the temperature to rise to 4.0. 2
This is a problem commonly encountered when trying to adjust K exactly and generally trying to switch smoothly between a low temperature mode and a high temperature mode. This means that any known prior art device can be used effectively to quickly adjust the amount of liquid present in the test chamber 15 and to smoothly transition its cooling power from hot to cold. Was originally impossible.

With the present invention, these disadvantages are obviated by obviating the need for a dedicated or intermediate condition for collecting liquid in the test chamber. If a low temperature mode of operation is to be achieved, a higher level of current is supplied to the heating element 14 and the feedback sensor 41 indicates when a predetermined high level, such as 300K, has been achieved. As described above, this operation effectively blocks the flow of liquid cryogen through capillary 13 and coupling tube 16 to the test chamber. This operation, in addition to providing a means for rapidly (less than 30 seconds) changing the helium flow required for the establishment of a high vacuum level in the test chamber 15 as required by the low temperature mode of operation. Using the dual impedance device shown in FIG. 2 results in a constant supply of cold liquid that provides the necessary cooling power to establish the temperature below 4.2K. Liquid collected via high impedance capillary 72 is thermally separated from helium reservoir 12 and reaches the test chamber at the desired reduced temperature (below 4.2K). Therefore, if the temperature is 4.
A stable environment is maintained at all times by automatically collecting liquid helium in the test chamber by the high impedance capillary 72 when lowered through 2K. At temperatures below 10K, only flow through the high impedance capillary 72, limited by wire 74,
Sufficient to provide cooling to regulate the temperature in the low temperature mode. This allows the user to smoothly transition the temperature through 4.2K in either the cooling mode or the heating mode, as shown in FIG.

In this low temperature mode, an adjustment is made to a valve that adjusts the vacuum level established by pump 38 depending on the desired temperature. If the operating temperature should be approximately 4.2K, the vacuum level at pump 38 should be about 736
does not exceed mmHg. If the temperature level at which the test is to be performed is approximately 1.5K, the vacuum level is about 1 mm
Hg or more. Of course, controller 75 has constant feedback on the level of vacuum. As described above, the highest level of vacuum is will be less than 1 mmHg, the relatively low equilibrium at about the boiling point of ⁴ the He, about 736
mmHg.

When operating in the high temperature mode, which is above 4.2 K, a suitably small current is sent to the heating element 14 while the temperature of the capillary 13 is read by the sensor 41. In general, it would be desirable to increase the temperature of the capillary to about 10K, which is high enough to boil the liquid as it flows through the capillary, but not high enough to significantly reduce the rate of mass flow therethrough. This temperature is about 10K
It is conveniently maintained by using a material for the temperature sensor 41 such as a resistive wire that conducts current in superconducting mode at a temperature less than. With such a wire, when in the superconducting mode, the electrical resistance of the sensor is almost zero.
The controller 75 determines the temperature of the capillary 13 by determining whether the sensor 41 is in its superconducting mode. This results in a cold fluid in gaseous form drawn into it by the underpressure created by the pump 38 into the test chamber 15, the level of which is precisely controlled by the controller 75. Pump 38
Note that the signal to includes a feedback signal from the pump 38 that provides constant information about the applied vacuum level. As described above, when operating in a high temperature mode in which gaseous cryogen is continuously applied to the test chamber 15, the vacuum level is very low, about 760 m.
mHg, approximately 200 cc / min. of helium gas.
1 ps maintained in the helium reservoir, producing a flow rate of
Operate effectively only at under pressure i. Thermal sensor 54 provides an input signal to controller 75, and current is provided to heating element 22 as shown in FIG. Thus, as the operator places the test chamber at the desired operating temperature, the controller 75 constantly reads the temperature in the test chamber (sensor 54) and provides additional heat as appropriate via the heating element 22. Typically, during high temperature operation, the vacuum level is determined to be appropriate to provide a continuous supply of a cryogenic fluid of gas to the test chamber;
This is not normally changed except when cooling to lower temperatures.

When the operator sets the operating temperature to, for example, 2.8 K, the program in the controller 75
3. Immediately apply a high current to the heating element 14 to interrupt the flow of cryogen through the heating element 3 and interrupt any current to the heating element 22 to approximately 381 mmHg or 7.2.
Active control in a feedback mode to determine the vacuum level to be applied by pump 38, such as psi absolute. If the desired operating temperature is 50K, the heating element 14 will be approximately 10K as described above.
And power will be applied to the heating element 22 to raise the temperature in the test chamber 15 to 50K as determined by the sensor 54. This is a constant feedback operation such that the controller 75 supplies current to the heating element 22 based on continuous readings from the sensor 54. At the same time, the vacuum level provided by pump 38 remains at a very low level, close to 760 mmHg.

It is possible to operate the device of the invention in a continuous transition mode between a low point and a high point, for example between 1.5K and 100K. In this mode of operation, the controller 75 always maintains temperature regulation at a movable temperature set point that smoothly rises to a target temperature specified by the user at means 77. For example,
1.5K to 100K at 100K target test temperature
There may be many set points calculated by the controller 75 according to the approach rate (K / min). Every time a set point or milestone is reached, a new one is established until the goal is reached. The control system 75 uses the information gathered from the temperature sensors 41 and 54 to move the actuators (heaters 14 and 22 and pump 38) to the target temperature at the rate desired by the user without having to pause at intermediate temperatures. And the vacuum level established by the valve in the test chamber). As a practical matter, the thermometer 54 needed to establish the desired temperature in the test chamber
By gradually opening the valve for adjusting the throughput using the feedback information from
Gradually changes the setting of the heater 22 and the vacuum level established by the pump 38. A dynamic aspect of the controller 75 is that the variable impedance capillary 13 can be shut off at different temperatures depending on the rate of temperature change as it approaches the 4.2 K boiling point. If cooling is achieved relatively quickly in the vicinity of 4.2K (typically at a rate higher than 7K / min), the heating element 14 as indicated by the sensor 54 when the test chamber 15 is at about 10K To a cutoff level of approximately 300K. However, if the cooling cycle is proceeding relatively slowly (at a rate of less than approximately 7 K / min), the capillary 1
An interruption of 3 may occur when the sensor 54 indicates about 6K. As mentioned above, the highest vacuum level will be in the range of 1 mmHg or more, but the balance at the boiling point of helium is about 73
It will be relatively low at 6 mmHg. Operating temperature is almost 4.
If it should be 2K, the flow of liquid through the high impedance inlet is sufficient to maintain temperature stability at vacuum levels not exceeding about 736 mmHg.

In order to repeat the operation of the device of the present invention at operating temperatures below the cut-off of the capillary 13, the cryogen in liquid form depends on how low the test temperature should be under relatively high vacuum. The test chamber is entered almost exclusively through the capillary 72. Above the blocking point of the capillary 13, substantially all of the cryogen enters the test chamber via the capillary 13 and is in a gaseous state. In the transition state, cryogen can enter the test chamber via both capillaries.

An important aspect of the present invention is the rate at which controller 75 can adjust the apparatus of FIG. 2 to achieve and / or maintain the desired temperature, or rate of temperature change, or both. In a continuous feedback loop,
The controller 75 takes readings from the sensor 54 in the test chamber and determines that the target temperature has a very tight tolerance (typically about 0.5
%) Or continuously adjust the level of vacuum or heat applied to the test chamber such that the temperature transition is performed without discontinuities.

Although heaters 14 and 22, sensors 41 and 54, and pump 38 are shown in singular, any of these may be multiple if required for operating speed or increased accuracy. May be included. Specific temperatures, pressures or other details are given by way of example only.

In view of the above description, those skilled in the art will perceive modifications and improvements of the present invention. The invention is limited only by the spirit and scope of the following claims, with due consideration given to the appropriate scope of equivalents.

[Brief description of the drawings]

FIG. 1 is a sectional view of a cryogenic container including a cryogenic liquid and a temperature adjusting device according to the present invention.

FIG. 2 is a sectional view of the device of the present invention.

3 is a simplified schematic diagram of the control part of the invention, showing the electrical connections to the electrical components of the device of FIG. 2;

FIG. 4 shows the temperature (Kelvin) for a typical prior art temperature regulator when lowering the temperature of the test chamber.
FIG. 4 is a plot of time versus time.

FIG. 5 is a plot of temperature versus time for the prior art apparatus of FIG. 4 as the temperature of the test chamber is increased.

FIG. 6 shows how to raise and lower the temperature of the test chamber.
FIG. 4 is a plot of temperature versus time for the present invention.

[Explanation of symbols]

 12 Cold reservoir 13 Capillary tube 15 Test chamber 72 Capillary tube

 ──────────────────────────────────────────────────の Continued on the front page (72) Inventor Stefano Spagna United States, 92037 California, La Holla, South Coast Boulevard, 921

Claims (16)

[Claims] 1. An apparatus for adjusting a temperature in a cryogenic test chamber, the apparatus comprising: a cryogenic vessel adapted to contain a reservoir of a liquid-phase fluid at a low temperature; Means for defining a chamber; defining a fluid flow path between the cryogenic fluid inside the cryogen vessel and the test chamber, and having an inlet end and an outlet end in fluid communication with the interior of the test chamber. A first fluid flow means, disposed in the cryogen vessel, connected between the inlet end of the first fluid flow means and the cryogenic fluid in the cryogen vessel; A first capillary having an impedance of; a capillary heater means in thermal communication with the first capillary; a test chamber heater means in thermal communication with the test chamber; A second capillary separated from the portion and having a second flow impedance much higher than the first flow impedance, wherein the cryogen and the test chamber are internal to the cryogen vessel. A second fluid flow means connected between; and evacuating the test chamber partially to selectively remove the first fluid flow means and the second fluid from the cryocontainer.
Exhaust means operable to draw fluid into the test chamber through the fluid flow means of the test chamber, wherein the test chamber extends into the cryogenic fluid when the device is operating, and Maintaining the first fluid flow means and the second fluid flow means below the surface of the cryogen in the cryogen in the cryogen at a level that is maintained in the cryogen. Maintained, equipment. 2. The apparatus of claim 1, further comprising control means connected to said capillary heater means, said test chamber heater means, and said discharge means. 3. The apparatus of claim 1, further comprising first temperature sensor means in thermal communication with said first capillary, wherein said first temperature sensor means has an output. 4. A second test chamber in thermal communication with the test chamber.
4. The apparatus of claim 3, further comprising a temperature sensor means, wherein the second temperature sensor means has an output. 5. A feedback to said capillary heater means, said test chamber heater means, said discharge means, said output of said first temperature sensor means and said output of said second temperature sensor means. Further comprising control means connected in an array, wherein the capillary heater means, the test chamber heater means and the discharge means are configured to output the first temperature sensor output according to a temperature setpoint established by the control means and the first temperature sensor output. The apparatus of claim 4, wherein the apparatus is controlled in response to a second temperature sensor output. 6. Apparatus according to claim 2, wherein said control means includes means for entering a temperature setpoint to be realized by said second temperature sensor means. 7. A method for adjusting a temperature in a cryogenic test chamber coupled to a reservoir of cryogenic fluid in a cryogenic vessel, the cryogenic vessel providing a first heater and fluid to the test chamber. A first capillary having a variable first flow impedance coupled thereto; and a second capillary having a stable second flow impedance substantially higher than a normal first flow impedance. Wherein the second capillary couples the fluid to the test chamber, further comprising a second heater in the test chamber, wherein there is an adjustable drainage device and a programmable controller, the method comprising: Establishing a target temperature for the test chamber in the control device; and activating the exhaust device to establish a predetermined underpressure in the test chamber. Sensing the temperature in the test chamber; selectively drawing a cryogenic fluid into the test chamber via at least one of two capillaries; the first heater; Selectively operating the two heaters and the discharge device to achieve and maintain the target temperature. 8. The target temperature is between about 1.5K and about 400K.
8. The method of claim 7, wherein the range is K. 9. The method of claim 1, wherein the target temperature is between about 1.5K and about 400K.
9. The method of claim 8, wherein the segments are in the range of K. 10. The method of claim 8, wherein the temperature in the test chamber is continuously shifted through the range. 11. The method of claim 7, wherein the controller changes the underpressure in the test chamber by adjusting the discharge device. 12. The method of claim 7, wherein the test chamber heater is operated to increase a temperature in the test chamber above a boiling temperature of the cryogenic fluid. 13. The method of claim 7, wherein the cryogenic fluid is converted to a gas phase before entering the test chamber when the temperature of the first heater is raised to a predetermined level. . 14. The method of claim 7, wherein the first capillary tube effectively prevents the flow of cryogenic fluid to the test chamber when the temperature of the first heater is raised to a level near room temperature. the method of. 15. The underpressure in the test chamber increases when flow through the first capillary is effectively prevented from drawing cryogenic fluid through the second capillary into the test chamber. 15. The method of claim 14, wherein the method is performed. 16. The method of claim 15, further comprising reducing a temperature in the test chamber below a boiling temperature of the cryogen by reducing an underpressure in the test chamber.